Heretofore, apparatuses have been devised for detecting faults in the insulation of electrical conductors or wires such as those used in telecommunications. U.S. Pat. No. 3,491,290, for example, discloses electrical circuit means for recognizing two or more closely adjacent insulation faults in a single wire. U.S. Pat. No. 3,548,302 teaches apparatus for detecting bare portions of insulated wire that exceed a selected size or number for a given wire length. U.S. Pat. No. 3,823,370 discloses a circuit for counting detected faults in the insulation of a wire and for actuating an alarm when the fault rate exceeds a selected number for a given length of wire. It thus is seen that the state of the art has now reached a significant degree of sophistication and maturity.
When a group of insulated wires are used in close proximity, such as where they are being stranded into a cable, the information concerning the integrity of insulation about individual wires, though available in detail, can still be insufficient or at least not as meaningful as is actually needed. For example, were the insulation about one wire in a cable is faulty while the insulation about the other wires stranded thereabout is not faulty, the electrical properties of the cable may remain unimpaired. This is because the insulation about the remaining conductors in proximity with the fault prevents any short circuiting between wires. Thus, if only information concerning the integrity of the individual wires is available cable may be declared unacceptable when in fact it is functionally sound. Furthermore, cable fault testing has heretofore usually been performed after stranding at a test station remote from the manufacturing line. Such off-line testing is quite burdensome and fails to permit on-line fault marking and repair. It therefore would be desirable to devise an apparatus and method for detecting the presence of adjacent faults in the insulation about a set of wires as they are being stranded into a cable of the fault type likely to lead to a functional impairment of the cable. It is this task to which the present invention is primarily directed.